1. Field of Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to an LCD device with improved high transmittance and wide-view-angle characteristics while without gray-level inversion at an inclined viewing angle.
2. Related Art
An LCD device controls the light transmittance by using the characteristic that liquid crystal (LC) molecules present different light polarization or refraction effects under different alignments, so as to produce images.
A twisted nematic (TN) LCD device has a good light transmittance characteristic but has an extreme narrow viewing angle as influenced by the structure and optical characteristic of the LC molecules. Therefore, it is a new type of breakthrough for the panel display technique that a display may possess the characteristics of wide-view-angle and high light use rate at the same time.
To solve the transmittance and viewing angle problems, a twisted vertical alignment model has been proposed by the inventor of the present invention, which endows the LCD device with advantages such as the high transmittance and the wide viewing angle. However, the LC molecules are aligned in a vertical alignment manner, so when the LC molecules are applied with a low voltage and the LCD device is watched at an inclined viewing angle, a gray-level inversion problem occurs, which causes the problem of color shift at an inclined viewing angle and influences a normal presentation of images of the LCD device.
This mode as an example may be obtained with reference to FIGS. 1A to 1E. FIG. 1A is a schematic view of azimuth angle and polar angle. FIG. 1B illustrates an electrode structure of a twisted vertical alignment mode. FIG. 1C illustrates V-T curves of LC at different inclined viewing angles (i.e. polar angles) when optical axis of an upper polarizer and a lower polarizer of a LC cell respectively set to be 0° and 90°. From FIGS. 1C to 1E, it is known that a gray-level inversion occurs at an inclined viewing angle of 55° in the situation of a low gray level voltage and an azimuth angle of 0° and 90°.
To eliminate the distortion of V-T curves of the inclined viewing angle, in the prior art, two or more alignment domains are formed in the same pixel, and the V-T curves of the inclined viewing angle in every domain are made to be complementary so as to eliminate the gray-level inversion characteristic. In practice, three specific methods are provided, which are explained as follows. In the first method, one pixel is divided into multiple display areas, and every display area forms a different voltage by means of capacitive coupling, thereby producing the alignment effect of multiple display areas. In the second method, one pixel is divided into multiple display areas and two thin film transistors are used to make each display area form a different voltage, thereby solving the gray-level inversion problem. In the third method, the pixel is divided into two or more display areas and an electronic barrier material is covered above a part of electrode of the display area, thereby producing the alignment effect of multiple display areas.
However, the methods for solving the gray-level inversion problem in the prior arts have complicated LCD device processes. In view of the above, it is the subject of the present invention to provide a simple method with improved high transmittance and the wide-view-angle characteristics while eliminating the gray-level inversion at an inclined viewing angle by producing different electrical fields in each display area, so that the LCD device can present optimal images.